Electromagnetic positioning system

ABSTRACT

In a machine having two relatively movable members, such as the bed and carriage of a machine tool, drive means for moving one of the members, and control means coupled to the drive means, a positioning system for changing the relative movement of the machine members after a predetermined distance has been traveled. A retentive member of magnetizable material, such as a steel tape or rod, is mounted on one of the machine members, for example on the carriage, and is disposed generally parallel to the direction of relative movement. A magnetic recording means is mounted on the other machine member for magnetizing the retentive member at a discrete point thereon corresponding to the relative position of the machine members at which movement is to be changed. This recording is sensed by means which develops an electrical signal for causing the machine control to change the movement, for example to stop the carriage.

United States Patent [1 Roy [ ELECTROMAGNETIC POSITIONING SYSTEM [76]Inventor: John R. Roy, 95 Bucynes Dr.,

North Tonawanda, NY.

127 Filed c sfit. 9, i971 [21] App]. No.: 178,900

Primary ExaminerB. Dobeck Att0rneyConrad Christel et al.

[ Nov. 20, 1973 [5 7 ABSTRACT In a machine having two relatively movablemembers, such as the bed and carriage of a machine tool, drive means formoving one of the members, and control means coupled to the drive means,a positioning system for changing the relative movement of the machinemembers after a predetermined distance has been traveled. A retentivemember of magnetizable material, such as a steel tape or rod, is mountedon one of the machine members, for example on the carriage, and isdisposed generally parallel to the direction of relative movement. Amagnetic recording means is mounted on the other machine member formagnetizing the retentive member at a discrete point thereoncorresponding to the relative position of the machine members at whichmovement is to be changed. This recording is sensed by means whichdevelops an electrical signal for causing the machine control to changethe movement, for example to stop the carriage.

8 Claims, 3 Drawing Figures 1 W 28 SYSTEM ClU7CL/arvd caNHor M0701?CON/P0! 26 36 40 24 SHEET 1 OF 2 INVENTOR- JOHN R. 190 Y BY 6W? BMATTORNEYS PATENTEDHDYQO I975 1 ELECTROMAGNETIC POSITIONING SYSTEMBACKGROUND OF THE INVENTION This invention relates to generally to thecontrol art,

BRIEF DESCRIPTION OF THE DRAWING FIGURES FIG. 1 is a block diagram of apositioning system acand more particularly to a positioning system for 5cording to the Presentinvemion;

changing the relative movement of machine members after a predetermineddistance has been traveled.

One area of use of the present invention is in controlling machines ormachine tools for cutting, drilling and the like, wherein a particularoperation is to be performed repetitively for a given number of times onthe same or on a plurality of workpieces whereupon the machine controlsare reset for a different operation. While the present invention will bedescribed with particular reference to such machine operations, forexample drilling a plurality of holes each of the same depth, it is tobe understood that the principles of the invention can be variouslyapplied.

Some controls for machines and machine tools of this general type whichare presently available include mechanical trip stops and limit switchesin the electrical system controlling the positions of the machinemembers. These controls can require many trial settings and adjustmentsbefore they will function properly. Other available control systemsinclude electronic pulse counting and feedback systems which can createpositioning errors when signals are missed or when spurious signalsenter into the system. Mechanical wear and backlash can affect theoperation of lead screws included in many machines which alsocan giverise to positioning errors. Furthermore many electronic positioningsystems are rather complex and accordingly considerably expensive.

SUMMARY OF THE INVENTION It is, therefore, an object of this inventionto provide a new and improved positioning system for changing therelative movement of machine members after a predetermined distance hasbeen traveled.

It is a further object of this invention to provide such a positioningsystem which is accurate, requires only a single setting or adjustment,and is relatively simple in construction and convenient and easy tomaintain.

It is a further object of this invention to provide such a positioningsystem capable of both changing the rate of relative movement as well asstopping the movement between machine members.

The present invention provides a positioning system for changing therelative movement of machine members after a predetermined distance hasbeen traveled wherein the relative position between the members at whichthe movement is to be changed is recorded on a member of magnetizablematerial carried by one of the machine members. The magnetic recordingthereafter is sensed when the machine members arrive at the point wheremovement is to be changed, for example slowed or stopped, whereupon anelectrical signal is produced to command the machine to cause thedesired change in movement.

The foregoing and additional advantages and characterizing features ofthe-present invention will become clearlyapparent upon a reading of theensuing detailed description together with the included drawing.

FIG. 2 is a schematic circuit diagram of a portion of the system of FIG.1; and

FIG. 3 is a fragmentary perspective view, partly diagrammatic, ofapparatus which can be included in the system of FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring now to FIG.I, 10 designates generally a machine having first and second relativelymovable members. In the present illustration machine 10 is a machinetool having a bed 12 and a carriage 14 to which a tool such as a drill15 is connected for operation on a workpiece or part 16. Bed 12 isstationary and carriage 14 is movable relative thereto by means of alead screw 18 connected to carriage 14 through a suitable mechanicalcoupling 19 and coupled through a clutch 20 to the output shaft 21 of adrive motor 22. Clutch 20 and motor 22 are controlled by a sequencer 24connected thereto by electrical lines 26, 28 respectively, andelectrical power for operating motor 22 and sequencer 24 is obtainedfrom a suitable supply or source (not shown). In addition, drill 15 isdriven by suitable means (not shown) included in machine 10. Theforegoing arrangement is illustrative of a typical and well-knownmachine tool arrangement to which the positioning system of the presentinvention is applicable. Because these machines are well-known and inwide-spread use, a detailed description thereof is deemed to beunnecessary. Furthermore, the foregoing arrangement is merelyillustrative of various types of machines and machine tools havingrelatively movable members, to which the present invention may beapplied.

In accordance with the present invention, a retentive member 30 ofmagnetizable material is mounted on one of the machine members, in thepresent illustration on the relatively movable member or carriage 14.The machine members 12 and 14 move in directions parallel to each otherin the present illustration. Member 30 is elongated and disposed so thatthe longitudinal axis thereof is generally parallel to the direction ofrelative movement of members 12, 14. A preferred material for member 30is steel, and it can have various forms such as a relatively thin tapeor a rod. Alternatively, member 30 could be of non-magnetic materialhaving a surface thereof plated or coated with magnetic material. In theillustration of FIG. 1, member 30 is in the form of a thin tape, mountedat each end thereof to carriage Mby suitable fasteners 31. These variousforms of member 30 together with an alternative arrangement for mountingmember 30 will be described in further detail presently.

The positioning system of the present invention further comprisesrecording means on the other machine member, i.e. on stationary bed 12,for magnetizing the recordable member 30 at a discrete point thereoncorresponding tothe relative position of the first and second machinemembers 12 and 14, respectively, at which relative movement is to bechanged. The positioning system further comprises sensing means on thesame machine member, i.e. on bed 12, for sensing the magnetic recordingon member 30 during relative movement of the machine members 12, 14 andfor producing an output signal in response thereto. According to apreferred mode of the present invention, the recording means and sensingmeans are provided by a magnetic recording and pickup head showngenerally at 34 in FIG. 1, the particular mode of operation of head 34being determined by a mode selection means 36 connected to head 34. Thepositioning system of the present invention also comprises means 40coupled to the sensing means, i.e. to head 34, and to the machine clutchand motor control or sequencer 24 whereby in response to a signalproduced by the sensing means, sequencer 24 is caused to change therelative movement between the machine members 12 and 14. For exam ple,the relative movement between bed 12 and carriage 14 can be speeded up,slowed down, or stopped completely by the system of the presentinvention.

FIG. 2 is a schematic diagram illustrating in detail a preferredelectrical circuit including head 34, selection means 36 and means 40.Head 34 comprises a core 45 having a winding 46. Means 36 for selectionthe mode of operation of head 34 comprises a double-pole double-throwswitch having a pair of arms 49, 50 to which opposite sides of winding46 are electrically connected. Arm 49 of switch 49 is movable between apair of contacts 51, 52 and arm 50 is simultaneously moved between apair of contacts 53 and 54. FIG. 2 shows switch 36 in the recording modewhere arm 49 engages contact 51 to connect one side of winding 46through a switch 56 and a line 57 to the positive terminal of a sourceof relatively low dc. voltage in the form of battery 59. In thisrecording position of switch 36, arm 50 engages contact 53 to connectthe other side of winding 46 through lines 61 and 62 to the negativeterminal of battery 59.

The circuit of control means 40 comprises a differential operationalamplifier indicated schematically at 65. One preferred form of amplifier65 is commercially available from Analog Devices, Inc. designated model40.! Amplifier 65 has negative and positive input terminals 66 and 67,respectively, an output terminal 68 and a pair of bias terminals 69 and70. Input terminals 66 and 67 are connected through resistors 72 and 73,respectively, to line 57 on which the positive voltage is available. Thejunction of input terminal 66 and resistor 72 is connected through avariable resistor 74 to contact 54 of switch 36. The junction of inputterminal 67 and resistor 73 is connected directly by a line 75 to switchcontact 52. Bias terminals 69, 70 are connected to lines 57 and 62,respectively, on which the positive and negative levels, respectively,direct voltage are available. Amplifier output terminal 68 is coupledthrough a capacitor 78 to negative input terminal 66. Output terminal 68also is connected to the control or base terminal 79 of a transistorswitch 80, the collector terminal 81 of which is connected to thepositive terminal of battery 59. The emitter terminal 82 of transistor80 is connected to one terminal of the control winding of a relay 83,the other terminal of which is grounded.

The relay plunger 84 operates a pair of switch contacts 86, 87 which, inturn, control the flow of electrical power to sequencer 24 to controloperation of the 7 same.

a source of alternating current 93 having a voltage of about 15 volts.The other side of winding 92 is connected through switch 94 and avariable resistor 95 to the other terminal of a.c. source 93.

The operation of the positioning system of the present invention will beillustrated by way of example where machine 10 is to drill a pluralityof holes, each of the same depth, either in the same workpiece or indifferent workpieces. The workpiece to be drilled, for example workpiece16 shown in FIG. 1, is positioned and mounted on machine 10, and themachine is operated to drill a hole to the desired depth. In the presentillustration, carriage 14 moves to the left in FIG. 1 relative to bed12, and the final position of carriage 14 relative to bed 12 correspondsto the desired depth of the hole in workpiece 16. At that point head 34is operated in the recording mode to make a magnetic recording on medium30 corresponding to that position. This is accomplished by placingswitch 36 in the recording position shown in FIG. 2 and by closingswitch 56 momentarily. Coil 46 is energized and the resulting magneticflux in and around the air gap between the pole pieces of core 45magnetizes a discrete portion of the surface of member 30 adjacent head34. Then carriage 14 is moved to the right in FIG. 1 and returned to itsinitial position, workpiece 16 is either moved or replaced by a newworkpiece, and then carriage 14 again is moved to the left in FIG. 1 tobegin drilling of the next hole. Switch 48 is moved to the senseposition at or prior to the beginning of this next machine operation.When head 34 reaches the location or point on member 30 which ismagnetized, the magnetic flux from the recording on member 30 changesthe magnetic state of the air gap of core 45 resulting in a change inthe flow of current in winding 46. This, in turn, is applied to theinputs of amplifier 65, and the amplified output turns on transistor tocause a flow of current through the winding of relay 83. Plunger 84 isoperated to close switch contacts 86, 87, and as a result, sequencer 24is operated to stop the movement of carriage 14 by disengaging clutch20. Machine 10 or sequencer 24 would be provided with a suitable controlto return carriage 14 after stopping thereof. Switch 48 is maintained inthe position corresponding to the sensing mode during the desired numberof drillings of the same depth When they are finished and it is desiredto make a new setting, the recording on member 30 is erased byenergizing head after carriage 14 has been moved to position therecording on member 30 adjacent or proximate head 90. Resistor isadjusted to vary the level of current to that which is required to erasethe recording on member 30.

It is within the scope of this invention to place two spaced-apartmagnetic recording on member 30, a first corresponding to the point atwhich the rate of travel between carriage l4 and bed 12 is to bechanged, i.e. slowed down, and a second at which the relative movementis to be stopped. As a result, carriage 14 can be 7 A preferred form ofsequencer 24 which has this capability is available from the AllenBradley Company and designated model PDQ 11.

Head 34 preferably is constructed to have an air gap in core 45 of about0.001 to about 0.002 inch which would be suitable for most machineapplications. Where extreme accuracy in the change of relative movementof the machine members is not required, the air gap can be enlarged toabout 0.004 or 0.005 inch so as to produce a strong and wide flux fieldincident on member 30 to minimize the change of the signal being missed.Core 45 can be laminated of suitable metal stampings or formed ofsintered ferrite. Erase head 90 would be of a construction somewhatsimilar to that of head 34, although head 90 would have a relativelylarger air gap and larger winding to accommodate the stronger electricalcurrent required for magnetic erasing. The record and pick-up head 34and erase head 90 are aligned on opposite sides of member 30 as shown inFIG. 2, and this arrangement permits selective erasure of a specificmagnetic recording for the purpose of making fine corrections oradjustments in the desired settings. In addition, either or both of theheads 34 and 90 preferably are spring-loaded to maintain sliding orwiping contact with member 30 as wear takes place.

The magnitudes of resistors 72 and 73 are determined by the effectiveelectrical resistance of head 34 so as to apply a suitable level of biasvoltage to winding 46 during the sensing mode. Variable resistor 74functions as a sensitivity selector for the purpose of compensating forany external electrical noise which may be present.

The system of the present invention is shown in FIG. 1 in a machinehaving one axis of movement. The system is readily adaptable to machineshaving a plurality of axes, simply by including additional retentivemembers 30 for each additional axis, along with the appropriatemodifications in the magnetic recording and sensing and electricalsignal producing components of the system. 1

FIG. 3 shows an arrangement for mounting member 30 in a typical machine10, and in particular on carriage 14. Member 30 here is in the form ofan elongated steel tape which preferably has a thickness of from about0.003 to about 0.005 inch. Tape 30 is supported in a frame 100 having abase portion 101 generally elongated and rectangular and having a pairof upstanding flanges 102, 103 at each end thereof. Base 101 is fixed tocarriage l4. Tape 30 is secured at each end thereof to correspondingones of flanges 102, 103 by mounting blocks 104 and 105, respectively,by bolts 106 or suitable fasteners. Frame 100 is formed from temperaturestabilized steel to minimize expansion and contraction thereof. Thiscompensates for flexing of tape 30 due to the fact that head 34 and head90,

the relative movement between machine members with apparatus which isrelatively simple in construction and easy to operate and maintain. Thesystem of the present invention can be installed easily and economicallyon most known machines. The initial setting of the system which isutilized in subsequent machine operations is made relatively quickly andoften requires no adjustments.

While a single specific embodiment of the present invention has beendescribed in detail, this has been done by way of illustration withoutthought of limitation.

I claim:

1. In a machine having first and second relatively movable members,drive means for moving one of said members, and control means coupled tosaid drive means, a positioning system for changing the relativemovement of said machine members after a predetermined distance has beentraveled, said system comprising:

a. a retentive member of magnetizable material mounted on one of saidmachine members, said retentive member being elongated and flexible;

b. recording means on the other of said machine members for magnetizingsaid retentive member at a discrete point thereon corresponding to therelative position of said first and second machine members at whichrelative movement is to be changed;

0. sensing means on said other machine member for sensing the recordingon said retentive member during relative movement of said machinemembers and for producing an output signal in response thereto;

d. means coupling said sensing means to said control means whereby inresponse to a signal produced by said sensing means said control meanscauses a change in the relative movement of said machine members;

e. a support frame mounting said retentive member on said machinemember, said frame being secured to said retentive member at oppositeends thereof to permit flexing thereof; and

f. magnetic erasing means on said other machine member, said erasingmeans being disposed toward a surface of said retentive member oppositethe surface toward which said recording means is disposed, said erasingmeans being substantially in alignment with said recording means.

2. A positioning system as defined in claim 1, wherein said first andsecond machine members move in directions parallel to each other andwherein said retentive member is disposed so that longitudinal axisthereof is generally parallel to the direction of relative movement.

3. A positioning system as defined in claim 1, wherein said controlmeans causes stopping of said relative movement when said sensing meansproduces an output signal.

4. A positioning system as defined in claim 1, wherein said controlmeans causes a change in the rate of said relative movement when saidsensing means produces an output signal.

5. A positioning system as defined in claim I, wherein said controlmeans decreases the rate of said relative movement in response to afirst signal from said sensing means and causes stopping of saidrelative movement in response to a second signal from said sensing meanswhereby said retentive member can be recorded at two spaced locationstherealong corresponding to the relative positions of said first andsecond machine members where relative movement therebetween is to bedecreased in rate and then stopped, respectively.

6. A positioning system as defined in claim 1, wherein said frame is oftemperature stabilized material.

7. A positioning system as defined in claim 1, wherein said recordingmeans and said sensing means comprise a core of magnetic material havingan air gap positioned adjacent said retentive member, a winding on saidcore, and switching means having a first position connecting saidwinding to a direct voltage source for 8 energizing said winding duringrecording and having a second position connecting said winding to asource of bias voltage and to said coupling means for sensing arecording on said retentive member.

8. A positioning system as defined in claim 7, wherein said couplingmeans comprises amplifier means connected to said switching means andrelay means connected in controlled relation to the output of saidamplifier means and in controlling relation to said machine controlmeans.

1. In a machine having first and second relatively movable members,drive means for moving one of said members, and control means coupled tosaid drive means, a positioning system for changing the relativemovement of said machine members after a predetermined distance has beentraveled, said system comprising: a. a retentive member of magnetizablematerial mounted on one of said machine members, said retentive memberbeing elongated and flexible; b. recording means on the other of saidmachine members for magnetizing said retentive member at a discretepoint thereon corresponding to the relative position of said first andsecond machine members at which relative movement is to be changed; c.sensing means on said other machine member for sensing the recording onsaid retentive member during relative movement of said machine membersand for producing an output signal in response thereto; d. meanscoupling said sensing means to said control means whereby in response toa signal produced by said sensing means said control means causes achange in the relative movement of said machine members; e. a supportframe mounting said retentive member on said Machine member, said framebeing secured to said retentive member at opposite ends thereof topermit flexing thereof; and f. magnetic erasing means on said othermachine member, said erasing means being disposed toward a surface ofsaid retentive member opposite the surface toward which said recordingmeans is disposed, said erasing means being substantially in alignmentwith said recording means.
 2. A positioning system as defined in claim1, wherein said first and second machine members move in directionsparallel to each other and wherein said retentive member is disposed sothat longitudinal axis thereof is generally parallel to the direction ofrelative movement.
 3. A positioning system as defined in claim 1,wherein said control means causes stopping of said relative movementwhen said sensing means produces an output signal.
 4. A positioningsystem as defined in claim 1, wherein said control means causes a changein the rate of said relative movement when said sensing means producesan output signal.
 5. A positioning system as defined in claim 1, whereinsaid control means decreases the rate of said relative movement inresponse to a first signal from said sensing means and causes stoppingof said relative movement in response to a second signal from saidsensing means whereby said retentive member can be recorded at twospaced locations therealong corresponding to the relative positions ofsaid first and second machine members where relative movementtherebetween is to be decreased in rate and then stopped, respectively.6. A positioning system as defined in claim 1, wherein said frame is oftemperature stabilized material.
 7. A positioning system as defined inclaim 1, wherein said recording means and said sensing means comprise acore of magnetic material having an air gap positioned adjacent saidretentive member, a winding on said core, and switching means having afirst position connecting said winding to a direct voltage source forenergizing said winding during recording and having a second positionconnecting said winding to a source of bias voltage and to said couplingmeans for sensing a recording on said retentive member.
 8. A positioningsystem as defined in claim 7, wherein said coupling means comprisesamplifier means connected to said switching means and relay meansconnected in controlled relation to the output of said amplifier meansand in controlling relation to said machine control means.